What operating System are you running? If snow leopard, boot from the installation disk and run Disk Utility's disk repair on the volume to check for errors. Your drive won't boot without the kernel. You will most likely need to reinstall your OSX.
If you have Lion or Later, try booting into recovery mode. If you are unable to, try booting into internet recovery and doing the same procedure as suggested above.
There is unfortunately not much to do if you do not know your operating system. If you have Lion (10.7.) or later, there is no installation disk. If you haven't upgraded your OSX since you purchased it, and you have a 2009 Macbook, my guess would be you have Snow Leopard (10.6).
See if you can boot into single user mode (command + S) and run the following steps outlined in this support article http://support.apple.com/kb/ts1417:
Use fsck if necessary
fsck is a command-line utility that may be able to verify and repair a disk. If you can successfully start up in Safe Mode or use Disk Utility while started up from a disc, you don't need to use fsck. Here are some situations in which fsck may be necessary.
- Your Mac OS X disc isn't available.
- Your optical drive isn't available.
- You can't start with a Safe Boot by holding the Shift key during start up.
Tip: If you use a Mac OS X Extended (Journaled) formatted volume, such as with Mac OS X 10.3 or later, you probably won't need to usefsck. If you do use it for any reason, please be aware that benignerror messages can appear.If you're not sure how your volume is formatted and you can't start up from your Mac OS X volume to find out, type the following command in a command-line interface and then press Return:diskutil info /
If you see "File System: Journaled HFS+" returned, you have aJournaled volume.
To use fsck, you must run it from the command line. Unlike using your mouse pointer to open an application to do something, you'll need to type a text command at the prompt (#) to tell fsck what to do. The Terminal application (/Applications/Utilities) and single-user mode are two examples of command-line interfaces in which you can type such commands. To use fsck:
- Start up your computer in single-user mode to reach the command line.
Note: If necessary, perform a forced restart as described in the Emergency Troubleshooting Handbook that came with your computer. On desktop computers, you can do this by pressing the reset/interrupt button (if there is one) or holding down the power button for several seconds. On portable computers, simultaneously press the Command-Control-power keys. If your portable computer doesn't restart with this method, you may need to reset the Power Manager.
- At the command-line prompt type:
- Press Return. fsck will go through five "phases" and then return information about your disk's use and fragmentation. Once it finishes, it'll display this message if no issue is found:
** The volume (name_of_volume) appears to be OKIf fsck found issues and has altered, repaired, or fixed anything, it will display this message:
***** FILE SYSTEM WAS MODIFIED *****Important: If this message appears, repeat the fsck command you typed in step 2 until fsck tells you that your volume appears to be OK (first-pass repairs may uncover additional issues, so this is a normal thing to do).
- When fsck reports that your volume is OK, type reboot at the prompt and then press Return.
Your computer should start up normally and allow you to log in.